Array stamping of carbon nanotubes and quantum transport in low-dimensional carbon nanotube-TMDC devices

In the first part of this thesis, we present a new approach to the fabrication of devices based on carbon nanotubes (CNTs) in the low disorder regime. Our fabrication method consists of growing CNTs on a transparent quartz chip and stamping them on an array of tens of devices. The quartz chip and the recipient chip are designed in such a way that during the stamping process the CNTs do not touch any substrate and stays suspended on the electrodes of the recipient devices. The parallel transfer of tens of CNTs highly increases the average number of usable devices per chip. The resulting CNT-based devices are characterized via transport measurements at different temperatures down to the milli-Kelvin regime. The separation of growth chip from the measurement chip allows one to freely choose the material for the electrodes, opening the way for the implementation of CNT-based devices with superconducting or ferromagnetic leads. It was suggested recently that Majorana Fermions should emerge in CNTs contacted with a thin superconductor which retains its superconducting gap in presence of large in-plane field. We demonstrate an all-dry technique for contacting CNTs with few-layer-thick flakes of niobium diselenide (NbSe2) as superconducting layered material of the family of the transition metal dichalcogenides. The choice of NbSe2 is motivated by its large critical in-plane magnetic field. We show that the NbSe2-to-CNT contact resistance is comparable to that observed for other methods. We discuss the temperature and magnetic field dependence of the quantum transport in our devices. Furthermore, we could observe long-range superconducting correlations in a few micrometer-long CNT which is encapsulated in stack of NbSe2 and hexagonal boron nitride. We show that a substantial supercurrent flows through the nanotube section underneath the NbSe2 crystal and through a two-micrometer long portion which is not in contact with it. As predicted for superconductors with a cross section in the nanometer range, the current-triggered collapse of superconductivity is mediated by resistance steps due phase slip center nucleation. The Ising superconductor NbSe2 is the ideal playground to examine the emergence of phase slip events. The exact nucleation position of phase slip lines in plain NbSe2 films is hard to predict and crucially depends on the individual sample. By patterning a one-dimensional constriction in NbSe2, the free energy barrier, which must be overcome to create a normal conducting region inside the superconducting 1D channel, will be sufficiently small. We demonstrate that as such fabricated nanowires still show superconducting features and that we can relate their origins to phase slip centers and lines

Die sprunggelenksnahe Unterschenkelfraktur im Kindes- und Jugendlichenalter

Einleitung: Sprunggelenksnahe Unterschenkelfrakturen zählen zu den häufigsten Verletzungen, die bei Kindern bisher kaum beziehungsweise pedographisch noch nicht ausführlich in der Literatur Bedeutung fanden. Bei operativer Versorgung zeigen sich bezüglich Patientenzufriedenheit, des funktionellen Ergebnisses und des radiologischen Befundes sehr gute Behandlungsergebnisse, jedoch können signifikante Gangbildveränderungen beobachtet werden. Die Ergebnisse aus dem Erwachsenenalter können aber nicht einfach in das Kindesalter übernommen werden. Nach einem Trauma am Bein stellen die klinische Untersuchung, Röntgen, Computertomographie bzw. Kernspinuntersuchung den ebräuchlichen Weg dar. Diese sind jedoch nicht ausreichend um die Komplexität des Ganges zu beurteilen. Fragestellung: Ziel dieser Untersuchung ist die vergleichende Analyse des Fußes sowohl intraindividuell zwischen unverletzter unterer Extremität und ehemals bei sprunggelenksnaher Unterschenkelfraktur im Kindes- und Jugendlichenalter osteosynthetisch versorgter Extremität, als auch interindividuell zu einem Normalkollektiv. Material und Methoden: Retrospektiv wurden insgesamt 37 Patienten (Durchschnittsalter 17,6 Jahre bei Nachuntersuchung) mit operativ versorgten sprunggelenksnahen Frakturen bei einer Latenzzeit (Unfalltag bis Nachuntersuchung im Mittel) von 62 Monate mit Fragebogen, klinischer Untersuchung und mit der dynamischen Pedographie (EMED-SF-4, Firma Novel GmbH, München, Deutschland) nachuntersucht. Als Vergleichsgruppe wurden im gleichen Altersbereich (10 bis 24 Jahre) gesunde Probanden (N=46) akquiriert. Aufgrund der besonderen Verhältnisse bei Kindern, insbesondere des Wachstums, wurden drei Altersgruppen gebildet (10-13, 14-17 und 18-24 Jahre). Ergebnisse: Alle befragten Personen sind mit der Therapie zufrieden, jedoch sind nur 25 Patienten schmerzfrei und 9 Leute können nicht dasselbe sportliche Level wie zuvor erreichen. Unter Verwendung eines Clinical Scores erreichen drei Patienten ein schlechtes klinisches Ergebnis (8%). Bei der komplexen Ganganalyse zeigen sich bei diesen drei Patienten Auffälligkeiten, bei allen anderen nicht. Bezüglich der Analyse der Fußfläche zeigt sich annährend Symmetrie bis auf beide Patienten mit schlechtem klinischen Ergebnis der ältesten Gruppe mit verkleinerter Fußfläche auf der verletzten Beinseite. Annähernd gleiche Kontaktzeiten weisen alle Patienten bis auf drei (zwei aus der schlechten Gruppe) mit einer stärkeren Verlängerung der Bodenkontaktzeit auf der unverletzten Seite auf. Es finden sich signifikante verminderte Spitzenkraftwerte auf der verletzten Seite im Seitenvergleich bei den 14-17 jährigen, auf der unverletzten bei den 18-24 jährigen Patienten mit gutem klinischen Ergebnis. Die mittlere Patientengruppe zeigt jedoch eine signifikante Entlastung der medialen Ferse auf der verletzten Seite hinsichtlich des Spitzendruckes im Seitenvergleich. Erhebliche Veränderungen bezüglich des Maximaldruckes, Relativimpulses und speziell berechneten Verhältnis-Indizes (MLF, FFI, VFI) weisen aber alle drei Patienten mit schlechtem klinischen Ergebnis auf. Interessanterweise weisen die Probanden ebenfalls zum Teil signifikante Veränderungen auf. Diskussion: Es kann aufgezeigt werden, dass die Patienten, wie die Vergleichsgruppe, asymmetrisch laufen, somit keine perfekte Symmetrie aufweisen. Jedoch muss man in ganz besonderem Maße beachten, dass die operativ versorgten Kinder sich zum Teil noch im Wachstum befinden und dieses je nach Zeitpunkt des Traumas Einfluss nehmen kann. Ferner ist zu bedenken, dass Asymmetrien in der Ganganalyse, wie bei den Probanden gefunden, nicht an klinische Beschwerden geknüpft sein müssen. Die drei Patienten mit schlechtem klinischen Ergebnis weisen jedoch erhebliche asymmetrische Gangmuster auf. Schlussfolgerung: Die Kombination aus einem Clinical-Score mit der kostengünstigen, nicht schmerzhaften dynamischen Pedographie kann Untersucherunabhängig zusätzliche Informationen bei stattgehabter älterer Sprunggelenksverletzung liefern. Schlechte Verläufe können so frühzeitig erkannt und beeinflusst werden. Die gefundenen Ergebnisse können bezüglich der dadurch frühzeitig entdeckten posttraumatischen Arthroseentwicklung als Fortschritt gesehen werden. Die vergleichende klinische und pedographische Analyse des Fußes zwischen unverletzter und ehemals verletzter unterer Extremität scheint mit zusätzlichem interindividuellen Vergleich zu einem Normalkollektiv auch in der Routineuntersuchung sinnvoll

An analysis of MRI derived cortical complexity in premature-born adults : regional patterns, risk factors, and potential significance

Premature birth bears an increased risk for aberrant brain development concerning its structure and function. Cortical complexity (CC) expresses the fractal dimension of the brain surface and changes during neurodevelopment. We hypothesized that CC is altered after premature birth and associated with long-term cognitive development. One-hundred-and-one very premature-born adults (gestational age <32 weeks and/or birth weight <1500 ​g) and 111 term-born adults were assessed by structural MRI and cognitive testing at 26 years of age. CC was measured based on MRI by vertex-wise estimation of fractal dimension. Cognitive performance was measured based on Griffiths-Mental-Development-Scale (at 20 months) and Wechsler-Adult-Intelligence-Scales (at 26 years). In premature-born adults, CC was decreased bilaterally in large lateral temporal and medial parietal clusters. Decreased CC was associated with lower gestational age and birth weight. Furthermore, decreased CC in the medial parietal cortices was linked with reduced full-scale IQ of premature-born adults and mediated the association between cognitive development at 20 months and IQ in adulthood. Results demonstrate that CC is reduced in very premature-born adults in temporoparietal cortices, mediating the impact of prematurity on impaired cognitive development. These data indicate functionally relevant long-term alterations in the brain’s basic geometry of cortical organization in prematurity

Synthesis of 1,1,2,2,3,3-hexamethyl-4,5-bis(methylene)cyclopentane

An efficient synthesis of the title compound 14 is reported, which employs the ZnCl2/Et2O catalyzed addition of acetyl chloride (4) to 2-methyl-2-butene (5) and the [3+ + 2] cycloaddition of the 1,1,2,3-tetramethylallyl cation to 2,3-dimethyl-2-butene as key steps

Insular dysfunction reflects altered between-network connectivity and severity of negative symptoms in schizophrenia during psychotic remission

Schizophrenia is characterized by aberrant intrinsic functional connectivity (iFC) within and between intrinsic connectivity networks (ICNs), including the Default Mode- (DMN), Salience- (SN), and Central Executive Network (CEN). The anterior insula (AI) of the SN has been demonstrated to modulate DMN/CEN interactions. Recently, we found that the dependence of DMN/CEN interactions on SN's right AI activity is altered in patients with schizophrenia in acute psychosis and related to psychotic symptoms, indicating a link between aberrant AI, DMN, CEN, and psychosis. However, since structural alterations of the insula are also present during psychotic remission and associated with negative symptoms, impaired AI interaction might be relevant even for psychotic remission and corresponding symptoms. Twelve patients with schizophrenia during psychotic remission (SR) and 12 healthy controls were assessed using resting-state fMRI and psychometric examination. High-model-order independent component analysis of fMRI data revealed ICNs including DMN, SN, and CEN. Scores of iFC within (intra-iFC) and between (inter-iFC) distinct subsystems of the DMN, SN, and CEN were calculated, compared between groups and correlated with the severity of symptoms. Intra-iFC was altered in patients SN, DMN, and CEN, including decreased intra-iFC in the left AI within the SN. Patients' inter-iFC between SN and CEN was increased and correlated with the severity of negative symptoms. Furthermore, decreased intra-iFC of the left AI correlated with both severity of negative symptoms and increased inter-iFC between SN and CEN. Our result provides first evidence for a relationship between AI dysfunction and altered between-network interactions in schizophrenia during psychotic remission, which is related to the severity of negative symptoms. Together with our previous results, data suggest specific SN/DMN/CEN reorganization in schizophrenia with distinct insular pathways for distinct symptom dimensions

Sequelae of premature birth in young adults

Background and Purpose Qualitative studies about the abnormalities appreciated on routine magnetic resonance imaging (MRI) sequences in prematurely born adults are lacking. This article aimed at filling this knowledge gap by (1) qualitatively describing routine imaging findings in prematurely born adults, (2) evaluating measures for routine image interpretation and (3) investigating the impact of perinatal variables related to premature birth. Methods In this study two board-certified radiologists assessed T1-weighted and FLAIR-weighted images of 100 prematurely born adults born very preterm (VP <32 weeks) and/or at very low birth weight (VLBW <1500 g) and 106 controls born at full term (FT) (mean age 26.8 ± 0.7 years). The number of white matter lesions (WML) was counted according to localization. Lateral ventricle volume (LVV) was evaluated subjectively and by measurements of Evans’ index (EI) and frontal-occipital-horn ratio (FOHR). Freesurfer-based volumetry served as reference standard. Miscellaneous incidental findings were noted as free text. Results The LVV was increased in 24.7% of VP/VLBW individuals and significantly larger than in FT controls. This was best identified by measurement of FOHR (AUC = 0.928). Ventricular enlargement was predicted by low gestational age (odds ratio: 0.71, 95% CI 0.51–0.98) and presence of neonatal intracranial hemorrhage (odds ratio: 0.26, 95% CI 0.07–0.92). The numbers of deep and periventricular WML were increased while subcortical WMLs were not. Conclusion Enlargement of the LVV and deep and periventricular WMLs are typical sequelae of premature birth that can be appreciated on routine brain MRI. To increase sensitivity of abnormal LVV detection, measurement of FOHR seems feasible in clinical practice

Polarized surface-enhanced Raman spectroscopy of suspended carbon nanotubes by Pt-Re nanoantennas

We present optical nanoantennas designed for applications that require processing temperatures larger than 800 degrees C. The antennas consist of arrays of Re/Pt bilayer strips fabricated with a lift-off-free technique on top of etched trenches. Reflectance measurements show a clear plasmonic resonance at approximately 670 nm for light polarized orthogonal to the strip axis. The functionality of the antennas is demonstrated by growing single-walled carbon nanotubes (CNTs) on top of the antenna arrays and measuring the corresponding Raman signal enhancement of selected CNTs. The results of the measurements are quantitatively discussed in light of numerical simulations which highlight the impact of the substrate

Coulomb Blockade Spectroscopy of a MoS2 Nanotube

Low-temperature transport spectroscopy measurements on a quantum dot lithographically defined in a multiwall MoS2 nanotube are demonstrated. At T = 300 mK, clear Coulomb blockade is observed, with charging energies in the range of 1 meV. In single-electron tunneling, discrete conductance resonances are visible at finite bias. Additionally, a magnetic field perpendicular to the nanotube axis reveals clear indications of quantum state transitions, with effective g factors consistent with published theoretical predictions

The AdvancedMachines Library: Loss Models for Electric Machines

This paper presents how losses of electric machines are modeled as an extension of the Mode-lica.Electrical.Machines library. The theoretical background of the different loss models is elaborated and a Modelica implementation – the Ad-vancedMachines Library – is presented. Additional examples demonstrate the usage of the library

Supercurrent diode effect and magnetochiral anisotropy in few-layer NbSe2_2

Nonreciprocal transport refers to charge transfer processes that are sensitive to the bias polarity. Until recently, nonreciprocal transport was studied only in dissipative systems, where the nonreciprocal quantity is the resistance. Recent experiments have, however, demonstrated nonreciprocal supercurrent leading to the observation of a supercurrent diode effect in Rashba superconductors, opening the vision of dissipationless electronics. Here we report on a supercurrent diode effect in NbSe$_2$ constrictions obtained by patterning NbSe$_2$ flakes with both even and odd layer number. The observed rectification is driven by valley-Zeeman spin-orbit interaction. We demonstrate a rectification efficiency as large as 60%, considerably larger than the efficiency of devices based on Rashba superconductors. In agreement with recent theory for superconducting transition metal dichalcogenides, we show that the effect is driven by an out-of-plane magnetic field component. Remarkably, we find that the effect becomes field-asymmetric in the presence of an additional in-plane field component transverse to the current direction. Supercurrent diodes offer a further degree of freedom in designing superconducting quantum electronics with the high degree of integrability offered by van der Waals materials.Comment: 18 pages, 12 figure